1. Field of the Invention
The present invention relates to a plane driving type electroacoustic transducer comprising a film of diaphragm with a conduction pattern formed thereon and a magnetic circuit.
2. Description of the Prior Art
The following description will describe a plane driving type electroacoustic transducer of t he prior art with reference to FIG. 10.
A plurality of rodlike magnets 3 are evenly or almost evenly spaced apart inside a case of yoke 1 having its top face as an open face. As is illustrated in the drawing, these magnets 3 are placed so that the magnetization directions of the neighboring magnets 3 are opposite, whereby the yoke 1 and the magnets 3 form a magnetic circuit.
A diaphragm 5 composed of a film 6 and conduction patterns 7 formed on the film 6 is provided to cover the open face of the yoke 1.
In FIG. 10 explaining the prior art, the conduction patterns 7 are provided on one surface of the film 6 alone. It should be appreciated, however, that the conduction patterns 7 may be provided on both the surfaces of the film 6 as occasion demands.
The conduction patterns 7 have portions 7a that intersect at right angles with magnetic fluxes developed across opposite polarities of the magnets 3.
Hence, as a current flows through the conduction patterns 7, the conduction patterns 7 exert a driving force at the portions 7a that intersect at right angles with the magnetic fluxes. In case that the current is an alternating current, the diaphragm 5 vibrates and the electroacoustic transducer functions as a loudspeaker.
Further, in case that the diaphragm 5 vibrates by aerial vibrations, a current is generated in the conduction patterns 7 and the electroacoustic transducer functions as a microphone.
However, the plane driving type electroacoustic transducer arranged as above has problems as follows.
(1) Because the diaphragm 5 is composed of an extremely thin film with the conduction patterns 7 formed thereon, a vibration damping effect of the film itself is so poor that problematic abrupt attenuation readily occurs.
(2) In order to function effectively as an electroacoustic transducer, it is preferable to extend the length and increase the count of the portions 7a that intersect at right angles with the magnetic fluxes of the conduction patterns 7. On the other hand, flexural rigidity in a direction (a direction indicated by a capital A in the drawing: magnetic gap direction) intersecting at right angles with the magnetic fluxes of the diaphragm 5 is large in comparison with flexural rigidity in a direction (a direction indicated by a capital B in the drawing) intersecting at right angles with the magnetic gap direction, and there is a significant difference in flexural rigidity between the two directions, which often adversely affects the vibrations of the diaphragm 5.
(3) In case that the conduction patterns 7 are formed on the both surfaces of the film 6, the conduction patterns 7 on the respective surfaces are formed at the same position as viewed through the surfaces. This makes the above-described difference in flexural rigidity between the directions A and B far larger.
(4) Because the film 6 forming the diaphragm 5 is so thin that the diaphragm 5 by itself cannot hold its shape, the diaphragm 5 needs to be given with a tensile force constantly during positioning and assembly, which results in poor workability.